1. Technical Field
The present disclosure relates generally to a seal for use in endoscopic surgery adapted to maintain a fluid-tight connection about an instrument inserted through a cannula. In particular, the disclosure relates to a seal member having elasticity and rigidity characteristics which facilitate its effective use.
2. Background of Related Art
Minimally invasive surgical procedures are performed throughout the body and generally rely on obtaining access to an internal surgical site through a small incision made in the skin of a patient. A cannula is a narrow tube, typically 5 to 13 mm in diameter, which is partially inserted into the small incision in the skin to hold the incision open. The cannula provides a portal or conduit between the surgical site and the exterior of the patient's body through which a surgeon may introduce the various surgical instruments required by the desired procedures.
A cannula assembly typically includes components adapted to maintain a seal across its opening at all times, i.e., prior to, during and subsequent to the introduction or removal of a surgical instrument. The need for a fluid-tight seal is apparent when considering laparoscopic procedures in which an insufflation gas, usually carbon dioxide, is introduced into the patient's abdomen under a slight pressure to separate the abdominal wall from the vital organs. The inflation of the abdominal cavity provides a space where a surgeon may introduce viewing equipment or maneuver instruments into position. The fluid-tight seal is needed in this context to prevent the escape of insufflation gas to maintain this viewing and working space.
A dual seal system may be used to prevent the escape of insufflation gas. A first type of “cannula” seal serves to provide the seal in the absence of an instrument, but is usually defeated as soon as an instrument is introduced. A second type of “instrument seal” is capable of making a fluid-tight connection with the instrument, but is usually defeated as soon as the instrument is withdrawn. Placing an instrument seal proximally in relation to a cannula seal will allow the two seals to cooperate to seal the cannula at all times. A flapper valve may be used as a cannula seal of the first type. This type of seal has a flap which normally closes the passageway through a cannula, but is forced to pivot open by the distal end of an instrument. The flap may be biased by a spring to close once the surgeon withdraws the instrument. Another type of self-closing valve used for this purpose is an elastomeric duckbill valve. This type of valve closes with the assistance of the positive pressure inside an insufflated body cavity which forces the distal faces of the duckbill into sealing abutment with each other. As discussed above, a flapper valve, a duckbill valve or other type of cannula seal typically will not prevent fluid losses once an instrument is in place within the cannula. Accordingly, an instrument seal of the second type is provided. A simple type of conventional instrument seal includes a relatively flat elastomeric member with an aperture sized slightly smaller than the instrument to be introduced. The elastomeric member stretches and bends to expand the aperture to accommodate the instrument.
An effective instrument seal will exhibit several characteristics, a few of which are listed here. First, of course, is the ability to maintain a fluid-tight connection with a surgical instrument as the instrument is being used. A surgeon will likely advance the instrument distally through the aperture of the instrument seal, manipulate the instrument with both radial and angular movements, and finally withdraw the instrument. Through all of this movement, the instrument seal must be flexible enough to allow the aperture to move and reshape itself appropriately to maintain the necessary fluid-tight connection. Second, it is important that the instrument seal not hinder the efforts of the surgeon in advancing and withdrawing the instrument. There is a friction force associated with moving the instrument while it is in contact with the aperture of the instrument seal. This friction force is sometimes called an insertion force or glide force and must be low enough such that manipulating the instrument is not awkward for the surgeon. Also, an effective instrument seal will provide radial support for an instrument. Adequate radial support will aid in stabilizing the instrument so a surgeon need not direct too much attention to holding the instrument in position while performing the surgical procedures. Additionally, it is important that the instrument seal have memory to return to its original shape and position after use. This feature can facilitate the insertion of subsequent instruments. Finally, because a single surgical procedure will often require many instruments dissimilar size, an effective instrument seal will be able to accommodate instruments having a wide range of sizes.
Design considerations intended to enhance some of these instrument seal characteristics may also enhance others. For example, features designed to give an instrument seal radial rigidity to provide radial support to an instrument are also likely to be helpful in providing an instrument seal with memory. On the other hand, many of these design considerations compete with one another. In particular, to provide an instrument seal with a sufficient closing force to maintain a fluid-tight connection with an instrument, an elastomeric member may be provided which has an increased cross sectional thickness about the aperture. The increased surface area in contact with the instrument will enhance the sealing characteristics, but at the same time will adversely affect the insertion and glide forces. An instrument seal designed to be extremely flexible in order to minimize insertion and glide forces may be ineffective in providing radial support to an instrument. Accordingly, an effective instrument seal is capable of balancing the competing design goals to allow for an effective fluid-tight seal to be maintained while not providing a difficult or awkward use.